Exhaust gas composition control system for internal combustion engines, and control method

ABSTRACT

The exhaust gas composition is sensed by a sensor which provides an electrical output signal which is appliied to an integral controller which controls the mixing device (fuel injection system or carburetor) which mixes air and fuel to provide the air-fuel mixture for the engine, in proper proportion for minimum noxious exhaust emission. In accordance with the invention, the integral controller integrates at a rate which is controlled by the speed of the engine. A speed-dependent pulse signal is derived, applied to a monostable multivibrator (MMV) which samples the signal applied to the integral controller, so that the integral controller will integrate only when it receives the sample signal, and hold the then obtained integrated signal until the next sampled signal is applied thereto.

O United States Patent 1 in] 3,875,907

Wessel et al. Apr. 8, 1975 [54] EXHAUST GAS COMPOSITION CONTROL3.745.768 7/l973 Zechnall et al. 60/276 SYSTEM FOR INTERNAL COMBUSTION5:1 23/32 EA ENGlNES AND CONTROL METHOD 317591232 9/1973 Wahl et [75]Inventors: Wolf wessel, Schwieberdingen; 3.782.347 l/l974 Schmidt et al.123/119 R Johannes Brettschneider. Ludwigsburg-Pflugfelden, both ofPrimary E.raminer-Manuel A. Antonakas Germany Assistant E.\'aminer.lamesW. Cranson [73] Assignce Robert Bosch Gmb Stuttgart Attorney. Agent, orFirm-Flynn & Frishauf Germ any [57] ABSTRACT 22 F] d: S t. 20. I973 l lep The exhaust gas composition IS sensed by a sensor PP .261 whichprovides an electrical output signal which is appliied to an integralcontroller which controls the mix- 30 F ing device (fuel injectionsystem or carburetor) which i l f Prlomy Dam mixes air and fuel toprovide the air-fuel mixture for 0k. 19. German) the engine in properproportion or m nimum noxious exhaust emission. in accordance with theinvention, 123/32 the integral controller integrates at a rate which isField "5 EA E I '9 R controlled by the speed of the engine. Aspeeddependent pulse signal is derived, applied to a monostablemultivibrator (MMV) which samples the signal applied to the integralcontroller. so that the integral References cued controller willintegrate only when it receives the sam- UNITED STATES PATENTS plesignal and hold the then obtained integrated signal 3.0!(1374 10/1971Eddy 204M T until the next sampled signal is applied thereto. 3.62l.826ll/l97l Chrestensen l23/l48 E 3.738.34l 6/1973 Loos 123/1l9 R C|a|m5- 3Drawmg 3" zl .L F? '1 F 1 v l [in 29 t 2 l l 23 3L r! o 30 -sz l 2o l lI ll l V I l S L 33 l 12 2s 7 l l 28 INTEGRATING CONTROL l i U) L1 IAMPLIFIER l 1 i i w 'tfieemsmm yl fi fi SWITCHING CIRCUIT PATENTEUAFRems FIGS PATENTEDAPR 81975 3875909 sir-1n 3 OF 3 PROCESS AND APPARATUSFOR SCAVENGING THE SWIRL COMBUSTION CHAMBER OF TWO-STROKE CYCLE INTERNALCOMBUSTION ENGINES BACKGROUND. OBJECTS AND SUMMARY OF THE INVENTION Thepresent invention relates to a process or method of purging orscavenging the swirl combustion chamber of a two-stroke cycle(hereinafter, two-cycle) internal combustion engine; and to an enginehaving at a least one cylinder which has such a swirl combustionchamber, a working chamber with at least one gas inlet and at least onegas outlet, and a swirl combustion chamber which establishes acommunication between the flow aperture and the working chamber, forcarrying out the process.

it is, therefore, an object of the present invention to effectscavenging of the swirl combustion chamber in all performance conditionsand with the lowest possible stream losses, in order to achieve a highperformance of the internal combustion engine while holding the emissionof noxious materials within low levels.

This as well as other objects are accomplished according to the presentinvention by causing the scavenging of the swirl combustion chamber bymeans of a fresh gas stream which is split-off during the scavengingprocess from the main scavenging stream prevailing within the workingchamber of the cylinder. The gas stream enters the swirl combustionchamber through one or several primary partial regions of the flowaperture after having been separated by one or several upstream edgesections of the edge of the flow aperture. The gas stream crosses itselflaterally in a transposed fashion within the flow aperture to effectthereby a reverse scavenging during which the old or exhaust gas streamsout of the swirl combustion chamber through at least a secondary partialregion of the flow aperture. The exhaust gas stream is situatedalongside the gas which enters the swirl combustion chamber, and,thereafter, combines with the main gas stream, that is, the gas streamswirling within the working chamber, toward the gas outlet or exhaustport.

it has been found that by the process and structure according to thepresent invention, a particularly effective scavenging of the swirlcombustion chamber is achieved during all engine load regimes, includingidling, as a result of which the old exhaust gas is completely or nearlycompletely scavenged from the swirl combustion chamber by the inwardlystreaming gas. It is also possible according to the present invention toachieve extremely low values of emission of noxious matter in theexhaust gases especially during partial loading and during idle. Theexhaust gas is preferably guided out of the swirl combustion chamberthrough the flow aperture and into the working chamber in such adirection. that it undergoes small deviation or essentially no deviationduring the scavenging process and in addition attaches itself to themain gas stream swirling in the working chamber so that both streamsflow directly together in the direction ofthe outlet or exhaust port ofthe engine cylinder. Thus, only minimum streaming losses occur duringscavenging of the swirl combustion chamber and the working chamber,thereby avoiding power losses, and, moreover, guaranteeing as a result ahigh specific power of the internal combustion engine.

According to a further preferred embodiment of the present invention, itis intended that the gas be introduced through a partial region locatedon one side of the flow aperture and that it then travels a loop-likepath which has a single axial component in the direction of the axis ofcurvature of the path.

According to another preferred further embodiment of the process andstructure according to the present invention it is provided that thefresh gas streams into the swirl combustion chamber through a middleregion of the flow aperture, and that as a result, the fresh gasdisplaces the old or exhaust gas from the swirl chamber and through theregions of the flow aperture situated on either side of the middleregion. In this embodiment, the fresh gas follows a loop-like path inthe swirl combustion chamber such that it has two mutually oppositeaxial components.

The gas inlet ports which lead into the working chamber of the enginecylinder may be constructed and arranged in the usual way such that thefresh gas scavenging stream, which is created within the working chamber during the scavenging process, has a stream compo nent which isdirected toward the cylinder head. The gas stream component so directedthen flows along the cylinder head in the direction of the edge regionof the cylinder, which is adjacent to the outlet port or ports. The flowaperture is located above the path traversed by this gas streamcomponent. It lies along the cylinder head so that the fresh gas streamsinto the swirl conv bustion chamber through a primary partial region orregions provided therefore in the flow aperture. The fresh gas thenlaterally displaces the old or exhaust gas which circulates within theswirl combustion chamber and causes this exhaust gas to consequentlyflow out of the swirl chamber and into the working chamber through oneor several secondary regions of the flow aperture while suffering onlyminimum streaming losses. In consequence of the chosen stream directionsof the fresh gases and the old or exhaust gases and of the gas streamprevailing within the working chamber, the exhaust gas streaming out ofthe combustion chamber combines with the main gas stream prevailingwithin the working chamber and together they stream toward the outletport or ports with minimum losses. Preferably it is intended that thefresh gas stream which is formed within the swirl combustion chamberduring the scavenging process defines a loop-like path. It is suitablethat during scavenging of the exhaust gas the fresh gas streams withinthe swirl combustion chamber in a single loop. In this way it ispossible to achieve a result according to which the exhaust gas isquickly and nearly completely scavenged from the swirl combustionchamber.

Conditions may expediently be chosen so that the exhaust gas has beenscavenged from the swirl combustion chamber before the outlet port orports of the engine cylinder are closed so that while the scavengingprocess is taking place, some of the fresh gas follows the exhaust gasout of the swirl combustion chamber through the secondary partial regionor regions of the flow aperture which have been previously passed by thepreceding exhaust gas. In this way an optimum scavenging of the interiorof the engine cylinder is achieved.

The two-cycle internal combustion engine which serves for theapplication of the process and structure according to the presentinvention is characterized by the fact that the flow aperture of theswirl combustion chamber of the engine cylinder is constructed andarranged in such a way that the fresh gas which reaches the flowaperture during the scavenging process streams into the swirl combustionchamber through one or several primary partial regions of the flowaperture but preferably through a single partial region of the flowaperture after having been separated or splitoff from the main gasstream flowing within the work chamber towards the outlet port or ports.The angle of separation or deviation is an acute angle. The secondarypartial regions of the flow aperture, on the other hand, which arelocated on the side of the primary partial region or regions, areconstructed and arranged in such a manner that they offer a smallerresistance to the gas streaming from the swirl combustion chamber thanto the gas streaming into the swirl combustion chamber. The secondarypartial regions are also constructed and arranged to guide the gasstreaming from the swirl combustion chamber in such a manner that it candirectionally attach itself to the main gas stream flowing towards thegas outlet port or ports without difficulty, and preferably without orwith only very little deviation.

According to the preferred further embodiment of the present inventionit can be advantageously provided that the upstream and downstream (withrespect to the direction of the fresh gas streaming through the flowaperture during the scavenging process) edge sec tions of the flowaperture in the primary partial region or regions are constructeddifferently than the edge sections in the secondary partial region orregions. In this preferred embodiment the primary partial region orregions of the flow aperture, which are limited by the differentlyconstructed edge sections of the edge forming the flow aperture, are soconstructed that they offer substantially less resistance to the influxof gas into the swirl combustion chamber than do the secondary par tialregion or regions, Moreover, the secondary partial region or regions ofthe flow aperture present a substantially lesser resistance to theefflux of gas from the swirl combustion chamber than do the primarypartial region or regions of the flow aperture, so that during thescavenging process the fresh gas flows completely or substantiallycompletely only through the primary region or regions into the swirlcombustion chamber and the gas which flows out of the swirl combustionchamber, which consists at least in the beginning of the scavengingprocess of exhaust gas, flows completely or substantially completelyonly through the secondary partial region or regions of the flowaperture. This effect may be enhanced by the suitable inclination of theflow aperture.

In some cases it may be sufficient if the primary and the secondarypartial regions of the flow aperture are constructed identically but arearranged in such a way that the fresh gas stream formed in the workingchamber during the scavenging process has the tendency to flow into theswirl combustion chamber more intensively through the primary partialregion or regions than through the secondary partial region or regions.This has the effect that the exhaust gas flows out of the swirlcombustion chamber during the scavenging process through the secondarypartial region or regions, In order to achieve this effect one can alsoprovide that the primary partial region is located at a part of theengine cylinder head which is very intensively swept by the fresh gasstream, while the secondary partial region or regions are located at aportion of the engine cylinder head which is less intensively swept ornot swept at all by the fresh gas stream; taking care, however, that thepressures prevailing in the working chamber near the flow apertureduring the scavenging process are such that the described scavengingprocess of the swirl combustion chamber is enhanced.

It can be preferably provided that the flow aperture has only a singleprimary partial region. Similarly it may be advantageously provided thatthe flow aperture has only a single secondary partial region. However,in many cases it may be suitably provided that the flow aperture hasseveral secondary partial regions, preferably two secondary partialregions and/or several primary partial regions, preferably two primarypartial regions.

In general it is particularly suitable to provide that the flow apertureis formed by a single penetration through the cylinder head connectingthe working chamber of the engine cylinder with the interior of theswirl combustion chamber. However, in many cases it can be suitablyprovided that the flow aperture is formed by at least two penetrations,in effect two apertures, located side by side at a distance from oneanother. ln the latter case it is particularly advantageous if eachaperture forms a primary partial region or a secondary partial region.In this way one or several of the available apertures serve for theinflux of fresh gases into the swirl combustion chamber, while the otheraperture or apertures serve for the efflux of gases from the swirlcombustion chamber during the scavenging process thereof.

The two-cycle internal combustion engine may be preferentially a sparkignition engine. However, the invention may be used to advantage evenwith two-cycle compression ignition engines, preferably two-cycle dieselengines.

In general it has been shown to be particularly advantageous if thevolume of the swirl combustion chamber is equal to approximately 40 to90% ofthe compression volume defined when the piston is at thetop-deadcenter. Within these extremes, however, the range of to 90% ispreferred and in particular the range of to Further, it is generallysuitably provided that the smallest open cross-sectional area of theflow aperture is equal to approximately 20 to of the maximum crosssection of the swirl combustion chamber. Within these extremes, however,the range of 40 to 90% is preferred and in particular the range of 60 to80%, and at most 35% of the cross section of the bore of the cylinder,i.e., of the volume swept by the piston. It is preferably provided thatthe swirl combustion chamber be at least essentially located above thepiston head of the piston, i.e., that it lie at least essentially withinan imaginary continuation of the cylinder volume whose diameter isdetermined by the diameter of the piston.

In a preferred embodiment of the present invention it is provided thatthe middle of the flow aperture has a different and preferably largerradial distance from the longitudinal axis of the engine cylinder thandoes the middle of the swirl combustion chamber.

It has been shown to be particularly advantageous if those edge sectionsof the flow aperture at which the fresh gas which streams into the swirlcombustion chamber during the scavenging process and the gas whichstreams out of the swirl combustion chamber are staggered and have radiiof curvature as small as is permissible by the thermodynamic loading inthe cylinder.

In many cases it is suitable to provide that those staggered sections ofthe edge of the flow aperture have an average smaller distance from thelongitudinal axis of the engine cylinder than the respectivelyoppositely lo cated edge regions of the primary or secondary partialopenings of the flow aperture and that in any case the mentioned edgeregions can advantageously have other dispositions with regard to thecylinder axis.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a top plan viewpartly in cross section of a cylinder of a two-cycle internal combustionengine according to one embodiment of the present invention;

FIG. 2 illustrates a partial elevational view in cross section throughthe cylinder of FIG. I taken along the section line 22 thereof;

FIG. 3 illustrates a partial elevational view in cross section throughthe cylinder of FIG. 1 taken along the section line 3-3 thereof;

FIG. 4 illustrates a cross-sectional view through the swirl combustionchamber of the cylinder of FIG. 2 taken along the sectional line 44thereof;

FIG. 5 illustrates a cross-sectional view through the swirl combustionchamber of the cylinder of FIG. 2 taken along the sectional line 5-5thereof;

FIG. 6 illustrates a top plan view partly in cross section of a cylinderof a two cycle internal combustion engine according to anotherembodiment of the present invention;

FIG. 7 illustrates a top plan view partly in cross section of a cylinderof a two-cycle internal combustion engine according to yet anotherembodiment of the present invention;

FIG. 8 illustrates a partial elevational view in cross section throughthe swirl combustion chamber of the cylinder of FIG. 7 taken along thesectional line 88 thereof;

FIG. 9 illustrates a partial elevational view in cross section throughthe swirl combustion chamber of the cylinder of FIG. 7 taken along thesectional line 99 thereof;

FIG. I0 illustrates a top plan view in cross section of a cylinder of atwo-cycle internal combustion engine according to still anotherembodiment of the present invention; and

FIG. II illustrates a top plan view in cross section of a cylinder of atwo-cycle internal combustion engine according to yet another embodimentof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In discussing the variousembodiments of the present invention. like parts are identified by likereference numerals for simplicity of discussion.

Turning first to the embodiment illustrated in FIGS. I 5, a cylinder 10is identified, which may be the only cylinder of a two-cycle internalcombustion engine, which. in turn. is not shown in further detail.Although only a single cylinder is shown, it should be understood thaton occasion this engine may have further similar or identical cylinders.Except for the novel construction ofthe cylinder head 11, the two-cyclefuel burning engine in question has the usual construction whichincludes a working chamber 20 which is scavenged in an especiallyadvantageous manner according to the principle of reverse scavenging.However, under other circumstances, different scavenging systems of theworking chamber 20 could be provided. In this embodiment, the reversescavenging of the working chamber 20 is a so-called Schnurle" reversescavenging, named according to the inventor, Mr. Schnurle.

The cylinder 10 includes: a cylinder block 12, equipped with coolingfins, a cylinder head 11; a piston 13 with a slightly convexly curvedupper outer surface or crown 14; a pair of gas inlet ports 15 which aresymmetrical and are symmetrically arranged with respect to a plane whichextends through the center of the inte rior of the cylinder; and asingle exhaust port 16 whose mid plane is the symmetry plane common toboth inlet ports 15. The cylinder block 12, the cylinder head 11 and thepiston 13 in assembly form the working chamber 20. The maximum volumewhich can be achieved by the working chamber 20 occurs when the piston13 is at bottom-dead-center.

According to the invention, the cylinder head II is equipped with avortex or swirl combustion chamber 17, in whose wall 19, a spark plug 18is mounted. The swirl chamber 17 communicates with the working chamber20 through a flow aperture 22. The flow aperture 22 has a slight heightand is preferably formed as a single penetration or opening. The swirlchamber I7 has an essentially spherical shape, although it should beunderstood that it can have other shapes. In many cases it canadvantageously have another shape, such as, for example, an oval orellipsoidal shape.

The spark plug 18 is situated at approximately the mid-height of theswirl chamber 17 above the broken or staggered edges 34, 35, which hasbeen demonstrated in many cases as particularly appropriate. However, itshould be noted that occasionally one can also place the spark plug 18at other locations in the wall of the swirl combustion chamber 17, forexample, diametrically opposite the flow aperture 22 is also a preferredlocation.

In spite of the fact that the swirl chamber 17 has been designated asthe combustion chamber, it is clear that combustion can also take placein the working chamber 20. It is expedient not to cool the swirlcombustion chamber 17 with cooling ribs, rather, in many cases, it ispreferably thermally insulated. Nevertheless, it should be understoodthat the swirl chamber 17 may also be cooled.

The cylinder head 11 includes an inner wall 24, which lies opposite theupper outer surface 14 of the piston 13. The inner wall 24 has aslightly concave curvature which has nevertheless a greater degree ofcurvature than the degree of curvature of the upper outer surface 14.For this reason, at the edge of the inner wall 24 there is defined aso-called squeezing zone 25 when the piston 13 is in its top-dead-centerposition. In this position there exists the least possible distancebetween the cylinder head inner wall 24 and the upper outer surface 14of the head of the piston 13, while the open distance between the pistonhead surface 14 and the inner wall 24 in directions which lead from thesqueezing zone 25 toward the flow aperture 22, increases steadily to amaximum value which occurs at the beginning of the edge of the flowaperture 22 where a guiding zone is formed in the vicinity of thetop-dead-center of the piston for the gas streaming into the swirlcombustion chamber 17. The guiding zone facilitates the streaming of gasinto the swirl combustion chamber 17 during compression. Actually theguiding zone is effective on the gas stream, somewhat before thescavenging process in the swirl combustion chamber begins, and has anadvantageous effect on the flow during the scavenging process in theswirl combustion chamber.

The two gas inlet ports are obliquely inclined upward in a directionaway from the exhaust port 16 so that the main streaming, which takesplace in this embodiment in the working chamber 20 during scavenging,assumes the directions shown approximately by the arrows. In thedirections shown, the process ofthe main streaming follows along thecylinder head and past the flow aperture 22.

The flow aperture 22 is constructed according to the present inventionto contain a primary partial region 26 and a secondary partial region 27located side by side, which are limited by the differently formed edgesections of the edge of the flow aperture 22. Each of the two partialregions 26 and 27 extends for approximately half the length of the flowaperture 22 in the direction of its longitudinal axis indicated by thereference numeral 29 in FIG. I. The edge section of the flow aperture 22assigned to the primary partial region 26 and which belongs to what willin the following be described as the edge, meaning thereby thecircumferential wall of the streaming aperture, extends fromapproximately the location 30 in a clockwise direction to approximatelythe location 31. The remaining edge section ofthe flow aperture 22 isassigned to the secondary partial region 27.

As can be seen most clearly in FIGS. 2-5, the edge section of the flowaperture 22 which is assigned to the primary partial region 26 isconstructed differently than the edge section of the flow aperture 22which is assigned to the secondary partial region 27. In this way afresh gas from the working chamber 20 streams into the swirl combustionchamber 17 during the scavenging process essentially only via theprimary partial region 26 0f the flow aperture 22 in the direction ofthe arrows shown. The fresh gas is thereby forced into a loop-likestream within the swirl combustion chamber I7. The loop-like stream hasan axial component which is parallel to the longitudinal axis 29. Inthis manner, the old exhaust gas which is present at the beginning ofthe scavenging process within the swirl combustion chamber 17 and whichhas the same rotational direction in the swirl combustion chamber as thefresh gas, which is introduced into the swirl combustion chamber, iscompletely or at least nearly completely displaced by the gas nowintroduced in the region of the swirl chamber which is located above theprimary partial region 26 of the flow aperture 22. It is displacedlaterally and streams completely or essentially completely only throughthe secondary partial region 27 of the flow aperture 22 in the directionof the arrows shown in FIGS. 2 and 3, where the direction of the exhaustgas stream is approximately tangential with respect to the rota' tionalstream within the swirl combustion chamber 17. The exhaust gas streamingout of the swirl combustion chamber 17 attaches itself without deviationor without substantial deviation to the main gas stream which isstreaming in the working chamber 20 to the outlet port 16. As soon asthe old exhaust gas has been completely or substantially removed fromthe swirl combustion 17 through the secondary partial region 27, thefresh gas which follows the old exhaust gas can also stream through thesecondary partial region 27 of the flow aperture 22 into the workingchamber 20.

Conditions have been selected so that the gas traverses substantiallyonly a single loop, exhibiting the above-mentioned axial componentduring the scavenging process, as it streams into and then out of theswirl combustion chamber 17, i.e., the fresh gas follows a somewhathelical stream with substantially only one loop. Of course, this doesnot exclude the possibility that portions of the gas perform more thanone loop during the scavenging process within the swirl combustionchamber 17. However, it is particularly advantageous, because of thelower streaming losses, to construct the flow aperture 22 in such amanner that, if possible, the gas performs only one loop with an axialcomponent during the scavenging process. Of course, even after thescavenging process is completed, and during the compression stroke, gasenters the swirl combustion chamber 17 from the working chamber 20 sothat the gas circulates within the swirl combustion chamber I7. It hasbeen shown that the described embodiment of the flow aperture 22 createsparticularly advantageous streaming conditions even during thecombustion stroke within the swirl combustion chamber 17 and theseconditions have advantageous effects on the combustion process afterignition.

In order to achieve the described streaming in the swirl combustionchamber, it is advantageous to equip that half of the edge of the flowaperture 22 which extends in a counterclockwise direction (FIG. I)approximately from location 32 to approximately location 33, with thesmallest radii of curvature as is permitted by the thermal and technicalproduction conditions, so that this half of the edge forms a firstupstream broken or staggered edge 34 for the gas which streams obliquelythrough the primary partial region 26 of the flow aperture 22; that is,for the gas which streams approximately tangentially into the swirlcombustion chamber 17, and a secondary upstream broken or staggered edge35 for the gas leaving the swirl combustion chamber 17 obliquely throughthe secondary partial region 27 of the flow aperture 22.

The staggered edge 34, which is assigned to the primary partial region26 and which extends approximately from location 32 to location 31, islocated higher than the staggered edge 35, which is assigned to thesecondary partial region 27, in the upstream direction, as seen in FIG.2. The latter extends approximately from location 31 to location 33. Thestaggered edge 35 borders, in this preferred embodiment, moreimmediately the working chamber 20 than does the staggered edge 34, i.e.the curvature of the staggered edge 35 begins immediately at thatopening of the flow aperture 22 which is lowest (as seen in FIG. 3). Bycontrast, a guide surface region 36 leads to the staggered edge 34.which is assigned to the primary partial region 26 of the flow aperture22. The guide surface region 36 forms an acute angle with a planeperpendicular to the longitudinal axis of the cylinder 10, as seen mostclearly in FIG. 2. This has the effect that the staggered edge 34, whichconnects to the guide surface region 36, is located at some distanceabove the working chamber 20.

The half of the edge of the flow aperture 22 which lies downstream andwhich extends in the clockwise direction approximately from location 33to location 32 in FIG. I is constructed in a manner which isparticularly evident from FIGS. 2, 3 and 5. There is included, adownstream edge section 37 of the flow aperture 22 which is assigned tothe secondary partial region 27 and which extends approximately fromlocation 33 to location 30. The section 37 has a convex curvature withrelatively large radii of curvature. A downstream edge section 39 isalso included. The section 39 extends appoximately from location 30 tolocation 32, and is as signed to the primary partial region 26. Thesection 39 has a convex curvature with radii of curvature which are assmall as the thermal and production technical conditions will permit. Aplane section 40 is connected to the convexly curved edge section 39.The plane section 40 is straight and lies within the plane of thesection of FIG. 2 and up to a location 41 where it leads into thespherical curvature of the swirl combustion chamber 17.

The embodiment of the edge of the flow aperture 22 which is describedabove. has the effect that the scavenging of the swirl combustionchamber 17 is produced by a reverse scavenging which crosses in the flowaperture and whose two directions are displaced laterally. The gasleaving the swirl combustion chamber 17 during the scavenging process isdisplaced from the gas which streams into the swirl combustion chamber17 in such a manner that these two gas streams are laterally displacedand cross one another within the flow aperture 22. As may be seenespecially clearly from FIGS. I and 2, the flow aperture 22 lies in thathalf of the cylinder 10 which also contains the outlet port 16. Theinlet ports I5, however. are located in the other half of the cylinder10. Furthermore. that half of the edge of the flow aperture 22 which isupstream. referring to the gas streaming through the flow aperture 22during the scavenging process. has a greater distance from the outlet 16than the downstream half of the edge. If one further views the mainstream present in the working chamber 20 during the scavenging process,then it is clear, that with reference to the plane of FIG. 2 itexperiences a deviation of approximately l80 from location 44 tolocation 45, and when one consideres the direction of rotation of this180 stream, then it is obvious from FIG. 2 that the direction ofrotation of the gas stream prevailing in the swirl chamber 17 during thescavenging process is oppositely directed.

As can be seen further from FIG. I, the plan of symmetry ofthe two inletports extends through the longitudinal axis of the work chamber 20 andapproximately through the center of the flow aperture 22. This plane.however, is not a symmetry plane of the flow aperture 22. In many casesthe center of the swirl combustion chamber I7 and/or of the flowaperture 22 could lie preferentially at some distance laterallydisplaced from the above-mentioned symmetry plane as is shown in anexemplary embodiment in FIG. 11.

If the two-cycle internal combustion engine considered here is an enginewith fuel injection, then the injection nozzle can be located in thewall of the swirl combustion chamber 17, preferentially in such a mannerthat the fuel injected during the compression stroke into the swirlcombustion chamber 17 remains completely or nearly completely in theswirl combustion chamber until the moment of ignition. For example, theinjection nozzle can be located diametrically opposite the spark plug18.

As can be seen particularly clearly from FIG. I, the longitudinal axis29 of the flow aperture 22 is approximately perpendicular to thesymmetry plane of the gas inlet ports 15, which plane bisects the outletport 16 and contains the longitudinal axis of the cylinder 10, so thatthe described scavenging of the swirl chamber 17 occurs as a consequenceof the construction of the edge of the flow aperture 22, where theaverage height of the flow aperture measured in the axial direction ofthe flow aperture is relatively small compared to the diameter of theswirl combustion chamber 17. This too has an advantageous effect on theachieved power increase and the decrease of emission of noxioussubstances. However, it is conceivable, that the height of the flowaperture 22 is chosen larger or smaller than in the shown exemplaryembodiment.

The exemplary embodiment of FIG. 6 which illustrates a sectional topview of an alternate embodiment of the swirl combustion chamber 17 ofFIG. 1 can be constructed in all essential details similar to theembodiment of FIGS. 1-5, except that the longitudinal axis 29 of theflow aperture 22' of the swirl combustion chamber 17 is inclined at anacute angle of approximately 50 to the longitudinal axis of the outletport 16 as viewed in the top view. Instead of this angle ofapproximately 50, of course, depending upon the requirements, otherangles could be used. preferably in the range of 20 60. Otherwise. theedge of the flow aperture 22' could be constructed similar to the flowaperture 22 of the exemplary embodiment of FIGS. 1-5. In the exemplaryembodiment of FIG. 6 (and also in the other exemplary embodiments) it isintended, as shown, that the center of the flow aperture is preferablyat a greater distance front the longitudinal axis of the cylinder 10than is the center of the sphere-like region of the swirl combustionchamber 17. Furthermore, the above-mentioned center of the swirlcombustion chamber 17, as well as the center of the flow aperture arepreferably located between a plane which contains the longitudinal axisof the cylinder 10 and is perpendicular to the common symmetry plane ofthe two inlet ports 15 and another plane which perpendicularly intesectsthe longitudinal axis of the outlet port 16 at the level of the inletorifice of the outlet port 16.

The fresh gas which streams through the swirl combustion chamber 17during scavenging in the exemplary embodiment of FIG. 6, also has anapproximately loop-like direction with an axial component and preferablyonly one loop.

In the exemplary embodiment of FIG. 7, the inlet ports 15 of thecylinder 10, are constructed and located according to the exemplaryembodiment of FIGS. l5, except that there are two separate outlet ports16 from the working chamber 20. The common symmetry plane of the inletports 15 which is now also the common symmetry plane of the outlet ports16, contains the longitudinal axis of the cylinder 10. This plane isalso a symmetry plane of the sphere-like region of the swirl combustionchamber 17 and of the flow aperture 22". The cross section of the flowaperture 22" in top view has a kidney-shaped form with the primarypartial region 26 in the sense of this invention being formed by acentral region thereof and the secondary partial region 27 in the senseof the present invention being formed by the two regions of the aperture22" on either side of the central region. During the scavenging process,a fresh gas flows into the swirl combustion chamber 17 and alsoexperiences a loop-like streaming. However. this fresh gas stream splitssymmetrically to both sides having oppositely directed axial componentsand as a result. the old gas present in the swirl comhus tion chamber 17streams from the two sides of the primary partial region 26 and out ofthe symmetrical two secondary partial regions 27 in such a manner thatthe exiting gas attaches itself without substantial deviation to themain stream prevalent during scavenging in the working chamber 20. Asmay be seen from FIG. 8, the upstream half of the edge of the flowaperture 22" is effectively constructed so that a staggered edge 34' ofthe primary partial region 26 is at a greater distance from the workingchamber 20 than the staggered edges 35 of the two secondary partialregions 27. A surface 36' inclined to the plane which is perpendicularto the longitudinal axis of the cylinder leads to the stag gered edge34'. This surface can be constructed similarly to the surface 36 of HG.2.

The staggered edges 35' which lie upstream, when referred to the gasstreaming through the flow aperture 22" and which are assigned to thesecondary partial region 27, also once more border practically on theworking chamber and have very small radii of curvature.

As may be seen especially clearly from FIG. 9, the half of the edge ofthe flow aperture 22" which lies downstream with reference to the gasesstreaming through the flow aperture 22. is constructed in such a mannerthat the center section 39' of this half edge. which is assigned to theprimary partial region 26. has a convex curvature with a very smallradius of curvature and begins immediately at the working chamber 20,whereas the edge sections 37'. which lie on both sides of the centersection 39 and which are assigned to the secondary partial regions 27,while also convexly curved. have relatively larger radii of curvature.

In some cases it has been found advantageous and useful not to form theflow aperture. as in the above exemplary embodiment. as a singleaperture connecting the working chamber 20 with the swirl combustionchamber 17. but rather to form several such apertures which re separatefrom one another. preferably such that when one or the other of theapertures serves the inlet of the fresh gas into the swirl combustionchamber. the other aperture or apertures substantially serve as theoutlet or outlets of the gases from the swirl combustion chamber duringthe scavenging process. FlGS. l0 and 1] illustrate two such exemplaryembodiments. and it can be seen that they are variants of theembodiments of FIGS. 7 and 6. In the embodiments of FIGS. 10 and 11. theprimary and secondary partial regions ofthe flow aperture are separatedby lands which is not the case in the exemplary embodiments of FIGS. 6and 7. In the embodiments of HG. 10 the total flow aperture is dividedby lands into three separate pene tration or apertures 50. 51 and 52, ofwhich the center aperture 52 forms the primary partial region of theflow aperture. i.e.. it serves for the influx of fresh gas during thescavenging process and is constructed suitably for this purpose. On theother hand. the two other apertures 50. 51 serve as the gas outlet fromthe swirl combustion chamber l7 during the scavenging process and aresuitably constructed for this purpose. The stream ing of fresh gasformed during the scavenging process in the swirl combustion chamber 17of the embodiment of FIG. it] conforms in principle to the correspondingstreaming of the exemplary embodiment of FIG. 7.

However. the fresh gas exiting from the swirl chamber 17 is laterallydisplaced from the gas streaming into the swirl chamber by the presenceof the two lands.

In some cases it might be desirable to construct the apertures 50 and 51so that they serve as fresh gas inlets to the swirl combustion chamber17, while aperture 52 is constructed so that it serves as a gas outletfrom the swirl combustion chamber during the scavenging process.

in the exemplary embodiment of H6. 11, the flow aperture of the swirlcombustion chamber 17 is formed by two separate penetrations orapertures 54 and 55, separated from one another by a small land. Theaperture 54, which lies closer to the longitudinal axis of the workingchamber 20, is constructed for the inlet of fresh gas during thescavenging process, while the aper ture 55 is constructed to serve asthe gas outlet from the swirl combustion chamber 17 during the scavenging process. The scavenging stream created in the swirl chamber 17 has aloop-like progress, just as it has in principle also in the exemplaryembodiment of FIG. 6. A single outlet port 16 is utilized and thesymmetry plane 47 of the two inlet ports 15 contains the axis ofsymmetry of the outlet port 16 as viewed in FIG. 11. The center of theswirl combustion chamber 17 lies laterally displaced at some distancefrom the symmetry plane 47 in such a manner that the symmetry plane 47approximately contains the center of the primary par tial region of theflow aperture. which is formed by the aperture 54, so that the mostintensive streaming region of the main gas stream forming at thecylinder head in the working cylinder 20 during the scavenging processacts upon the aperture 54.

The piston 13, shown in FIGS. 1 5, is preferably constructed as a pistonwith a slightly convexly curved top portion. It should be understood,however. that the invention is not limited in any way to thisconfiguration, but that in two-cycle internal combustion engines otherpiston shapes can and are utilized. for example, the piston may be adeflector piston, 21 flat piston or the like. The invention can also beused in opposed piston engines. Furthermore. as has already beenmentioned. instead of the scavenging process of working chamber 20.which is described in the exemplary embodiment of FIGS. 1-5, some otherscavenging process may be used in which a portion of the fresh gas fromthe main stream of fresh gas is introduced during the scavenging intothe swirl combustion chamber for the purpose of scavenging it.

As is obvious from the preceding specification, the purging orscavenging of the swirl combustion chamber is effected during thescavenging of the working chamber by a spit-off portion of the fresh gasmain stream prevailing in the working chamber. Therefore the scavengingstream prevailing in the working chamber has been designated as the mainscavenging stream and the scavenging stream prevailing in the swirlcombustion chamber has been designated as the secondary scavengingstream.

By way of example only. the dimensions. for purposes of the presentinvention, of a test engine according to FIGS. L5. which displayed anextremely small emission of noxious substances while exhibiting verygood power output. are as follows:

Engine: 'lwo stroke with loop scavenging (Schnurle type) Bore: 56 mmStroke: 50 mm Piston according to FIG. 2

Compression ratio: 6.8 1

Diameter of chamber 17: 27.5 mm

Flow aperture 22:

Distance between points 32 33: 20 mm Distance between points 30 31: I3mm Radius of 34 and 35: 0.1 mm (nearly sharp) Radius of 39: 0.2 mm

Radius of 37: mm

Average height of the flow aperture: 2.5 mm

Angle between plane 36 and a plane perpendicular to the axis of the boreof chamber 20 Length of the plane 36: ll mm In H6. 2, the verticaldistance between edges 34 and 35 is approximately 3.5 mm. In some cases,this disance may be larger or smaller. In a special case, this distancewas 0 which means that the plane 36 was extended from point 32 untilpoint 33 and the edges 34 and 35 were in line. The radii of at least oneof the edges 34, 35, 39 could be as small as possible, this means, thatthe temperature of the edges in operation cannot burn the edges.

A single loop of the scavenging stream in the chamber 17 is advantageousregarding the scavenging losses and the short time available for thescavenging.

Finally, it will be understood that according to the present invention,the fresh gas entering the working chamber and forming the main gasscavenging stream can contain fuel or not. in the first case, the fuelis mixed with the fresh air in any known manner before the air entersthe working chamber. In the latter case, the fuel can preferably beinjected into the swirl combustion chamber.

What is claimed is:

l. A process for scavenging a swirl combustion chamber of a two-strokecycle internal combustion engine having at least one cylinder includinga working chamber, a swirl combustion chamber, a flow aperture throughwhich the swirl combustion chamber communicates with the workingchamber, a single reciprocating piston, and at least one gas inlet portand at least one exhaust port in communication with the working chamberwhich are free of any valve control, the process comprising:

a. forming the flow aperture to include a plurality of partial regionslaterally adjacent each other and at least one upstream edge section;

b. forming the at least one inlet port and the at least one exhaust portin the cylinder wall in the vicinity of the bottom dead center of thepiston so that they are opened only when the piston is in its bottomdead center.

c. establishing a main scavenging stream within the working chamber froma gas entering the working chamber through the at least one gas inletport when the piston is at its bottom dead center; and

d. splitting-off a portion of the main scavenging stream also when thepiston is at its bottom dead center and as a result of the mainscavenging stream contacting said at least one upstream edge section tothereby effect redirection of said split-off portion of the mainscavenging stream through one of said plurality of partial regions andinto the swirl combustion chamber, said redirected split-off portion ofthe main scavenging stream effecting a reverse, cross scavengingaccording to which said split-off portion is laterally displaced withthe flow aperture so that the exhaust gases stream out of the swirlcombustion chamber alongside of said incoming split-off portion andthrough another one of said plurality of partial regions to thereaftercombine with the main scavenging stream flowing within the workingchamber toward the at least one exhaust port.

2. A process for scavenging a swirl combustion chamber ofa two-strokecycle internal combustion engine as defined in claim 1, wherein saidplurality of partial regions is formed to include at least one lateralregion, and wherein said split-off portion is redirected through saidlateral partial region so that it traverses a loop-like path within theswirl combustion chamber, said redi rected stream having a single axialcomponent in the direction of the axis of curvature of the path.

3. A process for scavenging a swirl combustion chamber of a two-strokecycle internal combustion engine as defined in claim 1, wherein saidplurality of partial regions is formed to include a middle region, andwherein said split-off portion is redirected through said middle regionso that it traverses a loop-like path within the swirl combustionchamber, said redirected stream having two opposite axial componentsthereby displacing the exhaust gases to either side of said middleregion and out of the swirl combustion chamber.

4. A process for scavenging a swirl combustion chamber ofa two-strokecycle internal combustion engine as defined in claim 1, wherein theexhaust gases stream out of the swirl combustion chamber separated fromthe split-off portion.

5. A process for scavenging a swirl combustion chamber ofa two-strokecycle internal combustion engine as defined in claim 1, wherein saidplurality of partial regions is formed to include at least one primarypartial region and at least one secondary partial region. and whereinsaid split-off portion is redirected through said at least one primarypartial region and the exhaust gases stream out of the swirl combustionchamber through said at least one secondary partial region.

6. In a two-stroke cycle internal combustion engine having at least onecylinder provided with at least one inlet port and at least one exhaustport which are free of any valve control, a cylinder head, a piston, aworking chamber defined by the cylinder, the piston and the cylinderhead, a swirl combustion chamber, and a flow aperture providingcommunication between the working chamber and the swirl combustionchamber, the improvement wherein the at least one inlet port and the atleast one exhaust port are located in the cylinder so that they areopened when the piston is at its bottom dead center, and wherein saidflow aperture is constructed to include at least one primary partialregion and at least one secondary partial region, said regions beingconstructed and disposed relative to each other in such a way that saidat least one secondary partial re gion presents a lesser resistance tothe movement of gas out of rather than into the swirl combustionchamber. as a result during scavenging of the cylinder a main gas streamwithin the cylinder upon reaching said flow aperture has a portionthereof split-off at an acute angle to the direction of said main streamand streams at least substantially into the swirl combustion chamberthrough said at least one primary partial region, said at least onesecondary partial region being disposed, when viewed in the direction ofsaid main gas stream, laterally to said at least one primary partialregion, said at least one secondary partial region serving to guide thegas leaving the swirl combustion chamber so that it attaches itself tosaid main gas stream with substantially no deviation and moves therewithin the direction toward the at least one outlet port.

7. A two-stroke cycle internal combustion engine as defined in claim 6,wherein said flow aperture is defined by an edge section having edgesectors which are located both upstream and downstream, with referenceto said main stream passing through said flow aperture, said edgesection being associated with said primary and secondary partialregions, with those edge sectors associated with said primary partialregion having a different construction than those edge sectorsassociated with said secondary partial region.

8. A two-stroke cycle internal combustion engine as defined in claim 6,wherein said flow aperture is defined by an edge section, the upstreamportion of which, with reference to said main stream passing throughsaid flow aperture, is equipped with staggered portions for the gaswhich streams into the swirl combustion chamber and the gas whichstreams out of the swirl combustion chamber, and wherein said staggeredportions are associated with said primary and secondary partial regions,with those staggered portions associated with said primary partialregion being further from the working chamber than those staggered portions associated with said secondary partial region.

9. A two-stroke cycle internal combustion engine as defined in claim 8,wherein those staggered portions associated with said secondary partialregion include at least one partial sector which is located at the levelof the orifice which lies in the direction of the top of the piston.

10. A two-stroke cycle internal combustion engine as defined in claim 6,wherein said flow aperture contains a single secondary partial region.

ll. A two-stroke cycle internal combustion engine as defined in claim[0, wherein approximately one-half of the flow aperture is constructedas a gas inlet for the swirl combustion chamber and the other half isconstructed as a gas outlet for the swirl combustion chamber.

12. A two-stroke cycle internal combustion engine as defined in claim 6,wherein said flow aperture is constructed to include a middle region andtwo further regions with one on each side of said middle region, saidmiddle region being constructed as a primary partial region and said twofurther regions being constructed as secondary partial regions.

13. A two-stroke cycle internal combustion engine as defined in claim 6,wherein said flow aperture is defined by an edge section includingconvexly curved sections associated with said primary and secondarypartial regions which are located downstream, with reference to saidmain stream passing through said flow aperture, said convexly curvedsections associated with said secondary partial region having asubstantially larger radius of curvature than said convexly curvedsections associated with said primary partial region.

14. A two-stroke cycle internal combustion engine as defined in claim 6,wherein said flow aperture is defined by an edge section which includesstaggered portions associated with said primary and secondary partialregions and has associated therewith a guiding surface leading to saidstaggered portions, said guiding surface being inclined at an angle withrespect to a plane normal to the longitudinal axis of the cylinder andbeing located upstream, with reference to said main stream passingthrough said flow aperture, with respect to said staggered portionassociated with said primary partial region.

15. A two-stroke cycle internal combustion engine as defined in claim 6,wherein the cross section of said flow aperture has an elongated formdefining a longitudinal axis which is inclined to the longitudinal axisof said outlet port.

16. A two-stroke cycle internal combustion engine as defined in claim 6,wherein the working chamber includes two gas inlet ports and one gasoutlet port, and wherein said gas inlet ports and said gas outlet portare symmetrical with respect to a symmetry plane containing thelongitudinal axis of the working chamber, said symmetry planeintersecting said flow aperture.

17. A two stroke cycle internal combustion engine as defined in claim16, wherein said symmetry plane intersects said flow apertureapproximately through the cen ter thereof.

18. A two-stroke cycle internal combustion engine as defined in claim 6,wherein the working chamber includes two gas inlet ports and two gasoutlet ports, and wherein said gas inlet ports and outlet ports are symmetrical with respect to a symmetry plane containing the longitudinalaxis of the working chamber, said sym metry plane intersecting said flowaperture.

19. A two-stroke cycle internal combustion engine as defined in claim18, wherein said symmetry plane inter sects said flow apertureapproximately through the center thereof.

20. A two-stroke cycle internal combustion engine as defined in claim15, wherein said symmetry plane extends approximately through the centerof said at least one primary partial region of said flow aperture.

2]. A two-stroke cycle internal combustion engine as defined in claim 6,wherein the middle of said flow aperture is displaced from thelongitudinal axis of the working chamber and is located in that half ofthe cylinder which contains said at least one outlet port of the workingchamber.

22. A two-stroke cycle internal combustion engine as defined in claim 6,wherein said flow aperture is formed as a single penetration connectingthe working chamber with the inside space of the swirl combustionchamber.

23. A two-stroke cycle internal combustion engine as defined in claim 6,wherein said flow aperture is formed as at least two displacedpenetrations.

24. A two-stroke cycle internal combustion engine as defined in claim 6,wherein the height of said flow aperture is substantially less than theheight of the swirl combustion chamber.

25. A two-stroke cycle internal combustion engine as defined in claim 6,wherein the entire flow aperture lies above the top of the piston.

26. A two-stroke cycle internal combustion engine as defined in claim 6,wherein the swirl combustion chamber is at least substantially locatedabove the top of the piston.

27. A two-stroke cycle internal combustion engine as defined in claim 6,wherein the volume of the swirl combustion chamber is approximately 40to of the volume of the cylinder when the piston is at itstopdead-center position.

28. A two-stroke cycle internal combustion engine as defined in claim 6,wherein the volume of the swirl combustion chamber is preferably 60 to90% of the volume of the cylinder when the piston is at itstop-deadcenter position.

29. A two-stroke cycle internal combustion engine as defined in claim 6,wherein the volume of the swirl combustion chamber is preferably 80 to90% of the volume of the cylinder when the piston is at itstop-deadcenter position.

30. A two-stroke cycle internal combustion engine as defined in claim 6,wherein the smallest open cross section of said flow aperture isapproximately 20 to 95% of the maximum cross section of the swirlcombustion chamber.

31. A two-stroke cycle internal combustion engine as defined in claim 6,wherein the smallest open cross section of said flow aperture ispreferably 40 to 90% of the maximum cross section of the swirlcombustion chamber.

32. A two-stroke cycle internal combustion engine as defined in claim 6,wherein the smallest open cross section of said flow aperture ispreferably 60 to 80% of the maximum cross section of the swirlcombustion chamber.

33. A two-stroke cycle internal combustion engine as defined in claim 6,wherein said flow aperture includes an edge region part of which isassigned to said primary partial region. said assigned edge region,being that region where said splitoff portion is generated, having achannel-shaped bay area surface associated therewith. with saidchannel-shaped bay area surface being formed in the cylinder head andextending to said assigned edge region in such a manner thatits depthincreases.

34. A two-stroke cycle internal combustion engine as defined in claim 6,wherein the piston at its top-deadcenter position defines along with thecylinder head a squeezing zone of the working chamber, said squeezingzone being defined to begin at the circumference of the piston top andextend inwardly towards the longitudinal axis of the cylinder and beconnected to a guide zone leading to said flow aperture and wherein theopen height of said guide zone increases from said squeezing zone towardsaid flow aperture.

35. A two-stroke cycle internal combustion engine as defined in claim 6,wherein the radial distance from the center of said flow aperture to thelongitudinal axis of the cylinder is greater than the radial distancefrom the center of the swirl combustion chamber to the longitudinal axisof the cylinder.

36. A two-stroke cycle internal combustion engine as defined in claim 6,wherein said flow aperture includes an edge section part of which isassigned to said primary partial region and another part of which isassigned to said secondary partial region, said part being assigned tosaid primary partial region being that region where said split-offportion is generated, both parts of said edge region having radii ofcurvature which are as small as is permitted by the thermodynamicloading in the cylinder.

37. A two-stroke cycle internal combustion engine as defined in claim 6,wherein said flow aperture includes an edge section part of which isassigned to said primary partial region and another part of which isassigned to said secondary partial region, said edge section assigned tosaid primary partial region having a first sector where said split-offportion is generated and an opposite sector, and said edge sectionassigned to said secondary partial region having a first sector and anopposite sector, and wherein said first sectors are located generally ata lesser distance from the longitudinal axis of the cylinder than saidopposite sectors.

38. A two-stroke cycle internal combustion engine as defined in claim 6,wherein the internal combustion engine is a spark-ignition engine.

39. A two-stroke cycle internal combustion engine as defined in claim 6,wherein the internal combustion engine is a self-igniting engine.

40. A two-stroke cycle internal combustion engine as defined in claim 6,wherein the internal combustion engine is a diesel engine.

1. Exhaust gas composition control system for internal combustionengines (10) having sensing means (12) sensing the composition ofexhaust gases from the engine; an integral controller (30, 16)integrating the sensed signal with respect to time and providing anoutput control signal; means (11), mixing and proportioning the air andfuel being applied to the engine, said output control signal from theintegral controller (13, 16) being connected and applied to saidproportioning means and controlling said mixing and proportioning meansto mix the air-fuel mass ratio which results in a predetermined exhaustgas composition as sensed by said sensor when the mixture is burned inthe engine; the improvement wherein the integral controller integratesin steps, or recurring pulses, or cycles; and means (S) are providedderiving a pulsed signal representative of engine speed (n), said pulsedspeed signal being applied to said integral controller (13, 16) tocontrol the rate of cyclical recurrence of integration steps thereof independence on engine speed to effect integration at a time-average ratedetermined by said speed signal.
 2. System according to claim 1, whereinsaid integral controller has a fixed integration rate.
 3. Systemaccording to claim 1 wherein said integral controller has apredetermined integration rate; said pulsed speed signal is a pulsedon-off signal having an on-off ratio which is dependent on speed; andsaid integral controller is controlled by the ON pulses of said speedsignal to effect integration at its predetermined rate during theON-pulses only.
 4. System according to claim 1 further comprising athreshold switch (14) connected to the output of the exhaust gas sensingmeans (12) and providing on-off sensing output signals when the sensedexhaust gas signal passes a pre-set limit; and a switching circuit (15)controlled by said engine speed signal (n), the on-off sensing signalbeing connected to said integral controller (16) through said switchingcircuit and being further modified by said switching circuit inaccordance with the speed of the engine.
 5. System according to claim 4further comprising a monostable multivibrator (36) controlled by saidengine speed signal (n) and providing output pulses at a raterepresentative of engine speed to form said pulsed speed signal; saidoutput pulses being connected to said switching circuit (15) tointerrupt the on-off sensing signal being applied to said integralcontroller (16) and command the integral controller to integrate thesensing signal only during occurrence of the output pulses from themonostable multivibrator (36).
 6. System according to claim 5 whereinthe integration rate of the integral controller (16) is fixed and theduration of integration per unit time is controlled by the number ofoutput pulses per unit time.
 7. System according to claim 5 wherein themixing and proportioning means comprises a fuel injection system, saidsystem including said means (S) deriving the engine speed representativesignal to control the integration time of the integral controller (16)in accordance with the repetition rate of fuel injection events of thefuel injection system.
 8. System according to claim 5 wherein saidswitching circuit (15) comprises a switching transistor (26) controlledby said monostable multivibrator (36); a pair of transistors (24, 25)connected to receive the on-off sensing output signal and respectivelyconductive during the ON, or OFF time, said switching transistor (26)being connected to said transistors (24, 25) of the pair to additionallycontrol their conduction and inhibit conduction theref during the OFFtime of the MMV (36).
 9. System according to claim 8 wherein a voltagedivider is provided having three resistors (29, 30, 31), and having twotap points formed between the junction of two respective resistors (29,30; 30, 31), one terminal electrode of the transistors, each, of thepair being connected to a respective tap point of the voltage divider;and conduction of the transistors is controlled by a connection to thebases thereof, said connection including a first connection to theon-off sensing output signal and a second connection to said switchingtransistor (26).
 10. Method of controlling the composition of theexhaust gases of an internal combustion engine which comprises the stepsof mixing air and fuel to prepare an air-fuel mixture for application tothe engine; sensing engine speed; sensing exhaust gas composition andderiving a sensing signal representative of said composition;controlling the relative proportion of air and fuel being mixed as afunction of (a) exhaust gas composition, (b) time, (c) engine speed;wherein said controlling step comprises integrating the sensed signal incyclically repetitive steps; and controlling the recurrence rate of saidrepetitive steps, and hence the integration rate as a function of enginespeed.
 11. Method according to claim 10 wherein the step of integratingthe sensed signal in cyclically repetitive steps comprises periodicallyintegrating said sensed signal at a fixed integration rate.
 12. Methodaccording to claim 10 wherein the step of controlling the recurrencerate of said repetitive steps includes controlling the duration ofinterruption of integration, between steps, as a function of enginespeed.
 13. Method according to claim 10, wherein the step of controllingthe recurrence rate of said repetitive steps comprises pulsing thesensing signal as a function of engine speed, and the integration stepcomprises integrating the pulsed signal.
 14. Method according to claim13 wherein the step of pulsing the sensing signal comprises periodicallysampling the sensing signal at a rate representative of engine speed,and the integrating step comprises integrating the sampled signal, withrespect to time, at a fixed rate, during said sampling periods.